Device for protecting brushholder studs

ABSTRACT

A cylindrical &#39;&#39;&#39;&#39;can&#39;&#39;&#39;&#39; is placed over the end of an insulated brushholder stud and is secured by an adhesive to entrap a resilient pad between the ends thereof. The &#39;&#39;&#39;&#39;can&#39;&#39;&#39;&#39; and pad combination provide protection to the insulation against damage from mechanical abuse.

United States Patent Ellis et al. Apr. 23,1974

[54] DEVICE FOR PROTECTING 2,615,954 10/1952 Mungovan 174/181 BRUSHHOLDER STUDS 3,026,433 3/1962 Mueller 2,451,969 10/1948 Mueller Inventors: William Joseph Ellis; John Klebo 2,426,815 9/1947 Burrus 310 239 Wentz, both of Erie, Pa.

[73] Assignee: General Electric Company, Erie, Pa. Primary Examiner R Skudy [22] Fil d; D 21, 1972 Attorney, Agent, or Firm-Dana F. Bigelow; Walter C.

1' 21] Appl. No.: 317,182 Bemkcp U-S- Cl. p I v [51] Int. Cl. H02k 13/00 [58] Field Of Search 310/219, 238, 239, 242, A cylindrical is placed over h d f an i 310/247; 306/30 33; 151/1405; 29/631; lated brushholder stud and is secured by an adhesive 248/22; 174/181 to entrap a resilient pad between the ends thereof. The can and pad combination provide protection to [56] References C'ted the insulation against damage from mechanical abuse.

UNITED STATES PATENTS Jones 310/239 5 Claims, 2 Drawing Figures DEVICE FOR PROTECTING BRUSHHOLDER STUDS BACKGROUND OF THE INVENTION This invention relates generally to brushholders for dynamoelectric machines and more specifically, to a protective device for insulated studs used therewith.

It is often desirable and convenient to support brushholders of a dynamoelectric machine from some part of the frame or housing. Thus it becomes essential to provide adequate insulation in order to prevent the grounding of current-carrying parts. It has been the practice to provide an insulating support having a metal part secured to the frame and another metal part secured to the brushholder. The two metal parts are held together through a dielectric material. This insulation has been molded using one of various insulating compounds, one of the latest methods being the application of a fluidized bed coating of an epoxy dielectric material. Always present is the problem of obtaining a mechanical connection between the parts capable of withstanding the severe clamping pressure and vibration forces, while at the same time maintaining an insulation capable of withstanding the voltages to which it is subjected. If the insulation is broken or cracked, its overall dielectric value will be reduced to a point where dielectric breakdown may occur. It has been found that a large portion of these failures that occur in service are caused by physical damage occurring to the insulation during periods of manufacture, assembly, alignment and/or disassembly. In some instances this mechanical abuse may be unavoidable, for instance where the practice is to pry against the insulated stud in order to obtain proper alignment of the brushholder assembly. The end surface of the insulated stud is particularly vulnerable to abuse and is the most common location of failures.

It is therefore an object of this invention to provide an insulated stud which will withstand a normal amount of mechanical abuse without subsequent failure of the insulation.

Another object of this invention is the provision for an insulated stud which will allow a specified clamping pressure to be applied thereto without seriously impairing its insulation characteristics.

Yet another object of this invention is the provision in an insulated stud for withstanding impact or prying force to the end surface thereof without attendant weakening or failure to the insulation.

A further object of this invention is the provision in an insulated stud for a protective process which is simple, economical and effective.

These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.

SUMMARY OF THE INVENTION Briefly, in accordance with one aspect of the invention a resilient pad or the like is placed at the end of the stud to be protected and a cylindrically shaped can is placed over the combination and secured to the stud by an adhesive or the like. The impact-sensitive insulation, and in particular the vulnerable end surface, is thus afforded a protective coating which will withstand normal mechanical abuse, and allow a sufiiciently large clamping torque to be applied and maintained. It allows normal mechanical abuse at the end of the stud such as is produced by impact or prying force in the process of adjusting the stud for proper clearance to the commutator or slip ring. To facilitate the process of installation a hole may be formed in the end of the cylindrical can to allow the escape of air when the can is placed over the stud.

In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternate constructions can be made thereto without departing from the true spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of the preferred embodiment of the invention as it appears in an operational installation.

FIG. 2 is a longitudinal cross sectional view of a preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Reference is made to FIG. 1 wherein the invention is shown generally at 10 as applied to studs 11 having an insulation 12 applied thereto. The studs 11 are inserted in holes 13 of a brushholder 14 of a conventional type and are typically secured in rigid relationship therewith by a force-fit installation. The studs 11, which are generally used in pairs in spaced parallel relationship as shown in FIG. 1, provide an interconnection between the brushholder 14 and a support device 16 adapted to be secured to a dynamoelectric machine (not shown). The brushholder 14 is thus electrically insulated from the frame or stator of the machine. Connection of the support device 16 to the studs 11 is commonly accomplished by clamps 17 extending around the cylindrical bodies of the studs and torqued to a predetermined value. Disposed between the surface of the insulation 12 and the clamp 17 of each stud is a protective can" or cap 18 encasing the supported end of the stud and a portion of the sidewalls thereof.

For a more detailed description, reference is made to FIG. 2. The stud 11 is an elongate cylindrical body having an end surface 19 and sidewalls 21. Its composition is generally steel so that a metal-to-metal relationship exists between the walls of its supporting end 22 and the brushholder l4. Proximate the other end thereof the insulation material 12 encases both the stud endsurface 19 and the stud sidewalls 21.

A preferred material for use as an insulator is an epoxy composition of fluid bed powders. The process of application is known in the art and involves first the heating of the stud to a predetermined temperature and then circulating an epoxy powder in a whirlwind manner around the stud to coat it with a thin (e.g., 1/16 in.) coating of dielectric material.

This insulation material is characteristically hard and brittle and very susceptible to cracking and chipping whenever severe mechanical contact is made therewith. In particular, the end layer 23 of insulation covering the end surface 19 and the surrounding edges is substantially flat and is very vulnerable to mechanical abuse. To protect the end layer 23 of insulation a resilient pad 24 or cushion is disposed thereon to absorb the impact of any forces or concentration of a prying force that are directed to it. A preferred material for such use has been flake mica discs having a slightly smaller diameter than the cylindrical stud 11. The mica cushions the epoxy insulation and is capable of withstanding moderately high temperatures to which the machine is exposed. It is not necessary for the pad to be a dielectric since the insulation coating 12 adequately serves the purpose. A soft metal such as aluminum can therefore be used as a pad material.

For the purpose of securing the pad, and more importantly to provide further protection to the insulation material 12, the metal can or cap 18, constructed of an aluminum material or the like, is placed over the pad so as to encapsulate its outer surface. The can 18 comprises a round end wall 27 and an adjoining cylindrical side wall 28 having an inside diameter slightly greater than the outer diameter of the stud and insulation combination. An adhesive 29 is preferably applied to the surface of the insulation 12 to secure the can 18 in its installed position. A polyester varnish has been found to be a suitable adhesive, and is preferably of the solventless type to facilitate assembly.

The can 18 is placed on the insulated stud such that its end wall 27 impinges on the pad 24 which is then in a close fit relationship between the end wall and the surface of the insulation end layer 23. Support for the end wall 27 against collapse is thus provided and a specific length for the finished stud is thus established.

To facilitate installation of the can and to aid in the adhesive hardening process an aperature 31 is preferably formed in the can end wall 27. Its principal purpose is to allow the escape of entrapped air when the can is applied to the stud.

The process of applying the protective covering can thus be accomplished in the following steps:

1. placing a resilient pad against the end wall of the insulated stud;

2. forming a hole in the end wall of an aluminum can;

3. applying an adhesive to the inner sidewalls of the can; and

4. placing the can over the end of the insulated stud so that its end wall impinges on the pad and its sidewalls closely surround the sidewalls of the insulated stud. The resultant covering provides improved impact resistance to the insulation layer, and allows it to withstand prying forces, and yet allows sufficient clamping pressure to be applied thereto by clamps of a supporting device.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An insulating stud for connection at a supported end to a support device in a dynamoelectric machine and at a supporting end to a brushholder, comprising:

a. an elongated cylindrical core;

b. a brittle insulating material encasing at least a portion of said core including an end surface of the supported end;

0. a protective cap disposed over said brittle insulating material having a cylindrical sidewall in closefit relationship therewith and an end wall in close proximity to said end surface; and

d. a resilient pad disposed in close-fit relationship between said end wall and said brittle insulating material encasing said end surface, wherein said cap and said pad provide protection for said brittle insulating material against damage from mechanical abuse.

2. An insulating stud as set forth in claim 1 and including an adhesive placed between said cylindrical core and said protective cap.

3. An insulating stud as set forth in claim 1 wherein said protective cap end wall has a hole formed therein to facilitate its installation.

4. An insulating stud as set forth in claim 1 wherein said brittle insulating material is an epoxy composition.

5. An insulating stud as set forth in claim 1 wherein said resilient pad is composed of flake mica. 

1. An insulating stud for connection at a supported end to a support device in a dynamoelectric machine and at a supporting end to a brushholder, comprising: a. an elongated cylindrical core; b. a brittle insulating material encasing at least a portion of said core including an end surface of the supported end; c. a protective cap disposed over said brittle insulating material having a cylindrical sidewall in close-fit relationship therewith and an end wall in close proximity to said end surface; and d. a resilient pad disposed in close-fit relationship between said end wall and said brittle insulating material encasing said end surface, wherein said cap and said pad provide protection for said brittle insulating material against damage from mechanical abuse.
 2. An insulating stud as set forth in claim 1 and including an adhesive placed between said cylindrical core and said protective cap.
 3. An insulating stud as set forth in claim 1 wherein said protective cap end wall has a hole formed therein to facilitate its installation.
 4. An insulating stud as set forth in claim 1 wherein said brittle insulating material is an epoxy composition.
 5. An insulating stud as set forth in claim 1 wherein said resilient pad is composed of flake mica. 